A liquid crystal optical element is known in which the distribution of the refractive index is changed according to the application of a voltage by utilizing the birefringence of liquid crystal molecules. There exists a stereoscopic image display device that combines an image display unit with such a liquid crystal optical element.
By changing the distribution of the refractive index of the liquid crystal optical element, the stereoscopic image display device switches between a state in which the image displayed on the image display unit is incident on the eyes of a human viewer as displayed on the image display unit and a state in which the image displayed on the image display unit is incident on the eyes of the human viewer as multiple parallax images. Thereby, a high definition two-dimensional pixel display operation and a three-dimensional image display operation are realized, where the three-dimensional image display operation includes stereoscopic viewing with the naked eyes due to the multiple parallax images. It is desirable to realize good optical characteristics of the liquid crystal optical element used in the stereoscopic image display device.